NL2014542A - A method and device for treating an effluent stream derived from one or more electrolysis cells. - Google Patents

Abstract

The present invention relates to a method for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water. The present invention furthermore relates to a device for treating an effluent stream originating from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water, which device supplies the necessary pumps, valves and pipes includes.

Description

Brief indication: Method and device for treating an effluent stream from one or more electrolysis cells.

Description

The present invention relates to a method for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water. Furthermore, the present invention relates to a device for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halide takes place by electrolyzing at least one halide compound dissolved in water, which device provides the required pumps, valves and pipes includes.

The European publication EP 0 110 033 discloses a method for working up brine solution in which an effluent stream withdrawn from the anode space is used. Said effluent stream is led to an anolyte recirculation vessel, the effluent stream from the recirculation vessel being led to a dechlorinator, whereafter the stream thus removed from chlorine constituents is mixed with concentrated brine, after which the thus processed brine is recycled and supplied as feed to the anode space.

U.S. Pat. No. 4,481,088 discloses that an effluent stream is formed from an anode space which is subsequently stripped of chlorine constituents in a dechlorinator after which the resulting stream is returned via an number of intermediate steps as anolyte liquor to the anode space.

Also the method disclosed in the US publication US 2009/0026084 shows that an effluent stream is withdrawn from the anode space which is then stripped of chlorine components, after which a number of subsequent steps take place to subsequently return the thus treated effluent stream to the anode space.

U.S. Patent No. 4,169,773 discloses an electrolysis method wherein anolyte is recycled and re-saturated before being returned to the anolyte compartment.

U.S. Pat. No. 4,839,003 discloses an electrolysis method in which a sodium chloride solution is stripped of magnesium and calcium before electrolysis is carried out.

U.S. Pat. No. 4,190,505 relates to a method for electrolysis of sodium chloride in an electrolytic cell subdivided by an cation exchange membrane into an anode chamber and a cathode chamber, wherein an aqueous solution of sodium chloride containing an iron cyanide complex is purified to the iron cyanide complex content. reducing therein to an amount not greater than 0.5 ppm before the solution is supplied to the anode chamber.

US publication US 2011/303549 relates to a method for producing chlorine, alkali metal hydroxide and hydrogen, wherein a brine solution is prepared after which alkaline precipitates from the brine in the presence of hydrogen peroxide or in the presence of at most 5 mg / l active chlorine with be removed with the aid of a filter of activated carbon. A portion of the remaining brine solution is subjected to an ion exchange step and then to a membrane electrolysis step, wherein at least a portion of the chlorine, alkali metal hydroxide, hydrogen, and brine is recovered. Part of the recovered brine is subjected to a chemical dechlorination step which is carried out with the aid of hydrogen peroxide, whereafter at least a part of the dechlorinated brine is reused in the process.

Devices for performing an electrolysis of a halide compound in an electrolysis cell are known per se from European patents EP1 298 231, EP 0 427 340 and EP 0958 407 in the name of the present applicant. From EP1 298 231 a device is known in which a plurality of electrolysis cells are electrically connected in series, each of which electrolysis cells is provided with a cell element, provided with lower electrolyte supply lines and with electrolyte collection and discharge lines located near the top thereof, and the gases produced during the electrolysis, a cathode compartment with a cathode and an anode compartment with an anode and a diaphragm or semipermeable membrane, wherein the electrolysis cells are compressed under bias between two end plates, so that each anode compartment and each cathode compartment together with the supply lines and the collection discharge lines as a completely built up. Other types of electrolysis cells are disclosed, for example, in U.S. Patent No. 5,064,514, U.S. Patent No. 5,082,543. the international publication WO 98/32900 and the German Offenlegungsschrift 199 10 639.

The aforementioned electrolysis cells are mainly used for the preparation by electrolysis of chlorine gas intended for chlorinating water, for example swimming pool water, drinking water or waste water.

As raw material for such electrolysis cells and devices, NaCl (table salt) is often used for the production of chlorine. In practice, this means that the anode space (+ pole) is fed with a saturated brine solution, for example with a concentration of approximately 300 g / liter. It is desirable here, mainly from the point of view of litigation, that the aforementioned concentration in the anode space does not decrease any further. Because of the aforementioned condition, a so-called spent anolyte stream flows out of the anode space that still has a significant brine concentration. The present inventor has thus found that the salt yield achieved here is not 100%. In practice, the spent anolyte stream is often discharged to the sewer in an appropriate manner, thus losing valuable starting materials. In addition, the present inventor has found that the spent anolyte stream must be viewed as an acid stream. Chemical analysis of the spent anolyte stream has shown that residual amounts of chlorine are also present. The finished anolyte stream also has a corrosive character and this solution smells of chlorine.

An object of the present invention is to provide a method for treating the spent anolyte stream in such a way that residual streams that are produced during the production of a halogen in electrolysis cells can be usefully reused.

More specifically, it is an object of the present invention to provide a method for increasing the salt efficiency, in particular in a process wherein production of a halogen takes place in one or more electrolysis cells by electrolyzing at least one halide compound dissolved in water. .

The present invention thus relates to a method for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water, the method comprising the following steps: ) withdrawing an effluent stream from the anode space of said one or more electrolysis cells, ii) mixing the effluent stream from step i) with an aqueous stream, iii) subjecting the mixed stream from step ii) to a treatment for removal of halide constituents, iv) supplying the halide constituents treated stream according to step iii) to the mixed stream from step ii) such that a circuit is formed in which the treated halide constituents stream after mixing with the aforementioned effluent stream, is again subjected to treatment for the removal of halide components.

One or more objectives are met by applying the aforementioned method. In particular, by applying a treatment to remove halide components, a residual stream is obtained which is less corrosive and less odor-causing. It will be clear that different effluent streams from different electrolysis cells can be combined and that the effluent stream thus combined is further processed according to the present method. As an example of components to be removed, in the embodiment in which a pickle solution (table salt) is used, consideration may be given, for example, to C10 'and HC10 and derivatives. The term "remove" is also understood to mean the conversion of components to desired components, in the embodiment of a brine solution (common salt), Cl 'ions are particularly mentioned herein. And such Cl 'ions can in turn be used in halogens production to be re-subjected to the electrolysis step in one or more electrolysis cells. There is thus an increase in the salt efficiency.

From the point of view of litigation, it is desirable that the flow rate of the stream subjected to halide component treatment be greater than or equal to the flow rate of said effluent stream taken from the anode space of said one or more electrolysis cells.

In a particular embodiment, it is preferable that the flow rate in the aforementioned cycle is at least 10 times, preferably at least 50 times, in particular preferably at least 100 times, in particular 500 times, greater than the flow rate of said effluent stream withdrawn to the anode space of said one or more electrolysis cells.

Suitable treatment for removing halide components is one or more treatments selected from the group consisting of using a catalyst, adsorption medium, absorption medium and halide neutralizing medium. Such treatments can be used as separate treatments, but in a special embodiment it is also possible that a combination of two or more treatments is used.

An embodiment of the halide component removal treatment comprises a step of contacting with activated carbon. The activated carbon can be in a column or reactor wherein the aqueous stream to be treated is supplied to said column or reactor. The content of halide in the stream exiting from said column or reactor will be reduced in relation to the stream supplied. Such columns or reactors are saturated after a certain process time and must then be regenerated.

Another embodiment of the halide component removal treatment comprises a step of dosing H 2 O 2. The dosing of hydrogen peroxide has a neutralizing effect on the halide components present in the aqueous stream to be treated.

In a particular embodiment, it is desirable that an aqueous basic stream be supplied to the aforementioned cycle. Such an aqueous basic stream serves in particular to increase the acidity of the aqueous stream, particularly when the treatment for removing halide components comprises a medium that is not resistant to aqueous streams with a low acidity.

As a suitable aqueous basic stream, an aqueous stream originating from the aforementioned one or more electrolysis cells can be mentioned, thus bringing about a useful integration between the electrolysis cells on the one hand and the said cycle on the other hand.

According to a particular embodiment, it is desirable that the aforementioned aqueous alkaline stream be supplied on the basis of measuring the pH value of a stream in said circuit, in particular to a stream before or after applying said treatment to remove halide components .

Said aqueous alkaline stream is preferably supplied to the mixed stream originating from step ii), thus effecting an intensive mixing of said streams.

In order to prevent accumulation of undesirable components and for discharging a residual stream into the environment, it is preferable that a purge stream is withdrawn from the aforementioned cycle.

Because of the acidity and concentration of odor-causing components, it is preferred that the transport of the aforementioned effluent stream, withdrawn from one or more electrolysis cells, to the location where step ii) takes place is effected under the influence of natural decay. The anode space of the electrolysis cell is generally under pressure, in particular to prevent the undesired escape of halide components into the environment, whereby a natural decay can cause the intended transport. For example, in such an embodiment, pumps are less desirable.

In a preferred form, a stream withdrawn from the circuit is supplied to said halide compound dissolved in water before said halide compound is subjected to electrolysis. The current thus extracted contains in particular components which can be subjected to electrolysis with which the so-called salt efficiency of the electrolysis cell can be increased.

To prevent harmful and undesired gases, it is preferable that the transport of said effluent stream, withdrawn from one or more electrolysis cells, to the location where step ii) takes place, without contact with the ambient air.

From the point of view of process management, quality control and safety for employees, it is preferable that the performance of the aforementioned treatment for the removal of halide components is measured by monitoring the flow thus treated, for example using a redox sensor.

The present invention further relates to a device for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water, which device provides the necessary pumps, valves and pipes wherein said device comprises a line for withdrawing an effluent current from the anode space of said one or more electrolysis cells, which line is led to a mixing device, said mixing vessel being connected via a line to a device for carrying out a treatment for removal of halide components, the discharge conduit of said member being connected to said mixing vessel to form a circuit.

In the aforementioned device, it is desirable that a drain line is included in the aforementioned circuit, that a line is included that is connected to a container in which the halide compound to be electrolyzed is located and that said circuit is provided with a supply line for supplying an aqueous basic stream , in particular that said supply line comes from one or more electrolysis cells.

From process control and safety, it is preferable that one or more sensors are located in the vicinity of said device, which sensors monitor the concentration of halide in the ambient air.

The present device finds application in particular in environments where gaseous halogens are desired, for example as a disinfectant for swimming pools or drinking water. As examples of halides, chlorides, or derived compounds thereof, can be mentioned.

The present invention will be explained below with reference to a drawing, which drawing, however, is not to be construed as limiting.

Figure 1 shows a schematic representation of a special embodiment of the present device 1, in which an electrolysis cell 2 consisting of two separate compartments 3, 4 separated by a permeable membrane 5 is used for the formation of chlorine, based on table salt. The use of common salt as a starting material for the electrolysis serves only as an example and other halides, or combinations and mixtures of halides, can also be used, for example potassium chloride. A pickle solution is thus supplied from holder 13 via line 14 to anode space 3 in which anode 6 is present. As a result of a chemical reaction, NaCl is converted into chlorine gas which is supplied via line 9 to, for example, a swimming pool, using venturi pump 10 and venturi 11. In cathode space 4, in which cathode 7 is located, hydrogen is formed which via line 8 is discharged. The formation of a lye solution also takes place in cathode space 4, the lye thus formed being discharged via line 16 to container 15. Electrolysis cell 2 is also provided with an aqueous stream 37, supplied via container 36. In anode space 3, so-called finished brine or effluent stream 12 is supplied to container 19, wherein effluent stream 12 has a low pH value and is also provided with chlorine components. In container 19, in which a quantity of water is already present, mixing thus takes place between effluent stream 12 and the aqueous stream present in container 19. The mixed stream is withdrawn from holder 19 and supplied via, for example, filter 20 and pump 21 to a member 23 for carrying out the treatment for removing halide components. The treatment for removing halide components can lead to the formation of a stream 24 in which the content of halide components has been reduced to a desired level. Said desired content can be such that a small residual amount of halide components can still be observed in stream 24. Stream 22 is thus treated in means 23 in such a way that the halide constituents present in stream 22 are removed to a considerable extent, thus creating a stream 24 treated in this way which may be returned to container 19 via filter 25, sensors 26-29, valve 30 and valve 32 The resulting cycle thus comprises the aqueous streams designated by reference numerals 22, 24, 31 and 34. Examples of sensors 26-29 may be mentioned sensors for measuring the pH, sensors for measuring the flow, sensors for measuring the flow. measuring the chlorine content. It is also desirable that there be one or more sensors in the room in which the present device is placed, which monitor the concentration of halide in the ambient air. When a certain limit value is exceeded, the operational management of the device is stopped, for example.

Valve 30 can be set such that part of stream 24 is returned to holder 13 via line 35. Valve 30 can be set such that part of stream 24 is returned to holder 19 via stream 31 and 34. Valve 32 can be set such that a part of stream 31 is withdrawn from the aforementioned cycle as purge stream 33.

In figure 1 it is also noticeable that formation of an aqueous basic stream 16 takes place in cathode space 4, wherein an aqueous basic stream is withdrawn from holder 15 via line 17 and subsequently supplied to holder 19. Holder 19 is also provided with a level sensor 18 with which level in container 19 is measured. If the level in holder 19 falls below or exceeds a preset value, sensor 18 will respond to this and the level in holder 19 will be restored to the desired value, for example by supplying or withdrawing an aqueous stream to holder 19 (not displayed).

The present inventor has carried out experiments with the arrangement shown in Figure 1, wherein the flow rate of the effluent stream 12 was set to a value of, for example, 3 liters / hour. The speed at which pump 21 was controlled in the above-mentioned cycle was such that the speed of the aqueous stream, indicated by 22, was approximately 1000 liters / hour. In such an embodiment, it is possible that valve 30 is adjusted such that the flow through line 35 is, for example, 2.7 liters / hour, valve 32 being adjusted such that the volume flow discharged as purge flow 33, e.g. 0.3 liters / hour amounts. The aforementioned values are for illustrative purposes only and should in no way be construed as limiting. The presence of filters and pumps, as included in the figure, is not to be construed as limiting.

The conduit emerging from the anode space 3, which is led to holder 19, flows into holder 19 in such a way that contact with the outside air is limited to a minimum. Furthermore, anode space 3 is placed under reduced pressure during operation, which also minimizes the escape of halide components such as gas. For the transport of the effluent stream 12 from electrolysis cell 2 to holder 19, it is desirable that electrolysis cell 2 is placed at a higher level than holder 19 so that the transport of the effluent stream 12 can take place under natural decay.

The description of the figures discussed above is for illustrative purposes only and does not limit the scope of the present invention, which scope is defined by the appended claims.

Claims (21)

A method for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water, characterized in that the method comprises the following steps: i) withdrawing an effluent stream from the anode space of said one or more electrolysis cells, ii) mixing the effluent stream from step i) with an aqueous stream, iii) subjecting the mixed stream from step ii) to a treatment for removing halide components, iv) supplying the halide component-depleted stream treated according to step iii) to the mixed stream from step ii) such that a circuit is formed in which the treated halide-component depleted stream is resumed after mixing with the aforementioned effluent stream subjected to halide berry removal treatment tooth parts. Method according to claim 1, characterized in that the flow rate of the stream subjected to a halide component treatment is greater than or equal to the flow rate of said effluent stream withdrawn from the anode space of said one or more electrolysis cells. Method according to one or more of the preceding claims, characterized in that the treatment for removing halide components comprises one or more treatments selected from the group of using a catalyst, adsorption medium, absorption medium and halide neutralizing medium. Method according to claim 3, characterized in that the treatment for removing halide components comprises a step of contacting with activated carbon. A method according to claim 3, characterized in that the treatment for removing halide components comprises a step of dosing H 2 O 2. Method according to one or more of the preceding claims, characterized in that an aqueous basic stream is supplied to said cycle. The method according to claim 6, characterized in that said aqueous alkaline stream originates from said one or more electrolysis cells. Method according to one or more of claims 6 to 7, characterized in that the supply of said aqueous basic stream takes place on the basis of measuring the pH value of a stream in said cycle, in particular on a stream before or after applying the aforementioned treatment to remove halide components. The method according to one or more of claims 6 to 8, characterized in that said aqueous basic stream is supplied to the mixed stream from step ii). Method according to one or more of the preceding claims, characterized in that a purge current is withdrawn from said cycle. A method according to one or more of the preceding claims, characterized in that the transport of said effluent stream, withdrawn from one or more electrolysis cells, to the location where step ii) takes place under the influence of natural decay. Method according to one or more of the preceding claims, characterized in that a stream withdrawn from the circuit is supplied to said halide compound dissolved in water before said halide compound is subjected to electrolysis. Method according to one or more of the preceding claims, characterized in that the transport of said effluent stream, extracted from one or more electrolysis cells, to the location where step ii) takes place, without contact with the ambient air. Method according to one or more of the preceding claims, characterized in that the performance of said treatment for removing halide components is measured by monitoring the stream thus treated. Method according to claim 14, characterized in that the monitoring takes place using a redox sensor. 16. Device for treating an effluent stream from one or more electrolysis cells, in which electrolysis cells production of a halogen takes place by electrolyzing at least one halide compound dissolved in water, which device comprises the necessary pumps, valves and pipes, characterized in that said device comprises a line for withdrawing an effluent current from the anode space of said one or more electrolysis cells, which line is led to a mixing device, said mixing vessel being connected via a line to a device for carrying out a treatment for removing halide components, wherein the discharge line from said member is connected to said mixing vessel to form a circuit. Device as claimed in claim 16, characterized in that a drain line is included in said circuit. Device as claimed in one or more of the claims 16-17, characterized in that a conduit is included in said circuit which is connected to a holder in which the halide compound to be electrolyzed is located. Device as claimed in one or more of the claims 16-18, characterized in that said circuit is provided with a supply line for supplying an aqueous basic stream. Device as claimed in claim 19, characterized in that said supply line comes from one or more electrolysis cells. Device as claimed in one or more of the claims 16-20, characterized in that one or more sensors are located in the vicinity of said device, which sensors monitor the concentration of halide in the ambient air.